Start then stop

Car is in excellent condition and drives like a dream. Never had any major problems. Serviced regularly. Was starting fine until the last service. Since then the car will start first time as usual but the instant dies out. I need to to turn the engine several times with the accelerator pressed down to get it started. Once it starts, and after a few revs, it will be fine driving. However, if it rest for three hours or more, the same trouble starts all over again. I have had it at the garage but they have not been able to solve the problems. They told me they had expelled air from the filter. Yesterday, they worked on it again and removed and installed the filter again. Now it is worse. Leaving the car resting for less than an hour causes the same start problem. I believe it's definitely the filter.

It's an Astra estate diesel 2002 2 liter engine.

Any advice will be appreciated.
Ray

P.S. The car is in Mauritius where I have an apartment. I brought it from Scotland.